Power boosters operating on a pressure differential, such as exists between the engine intake manifold of a vehicle and the atmosphere, are well known devices. Typically, a shell-like housing encloses at least one variable pressure chamber that is separated from a vacuum chamber by a diaphragm and its supporting wall. The diaphragm and supporting wall are axially moveable relative to the housing under variable pressure conditions. Often, the housing's interior is subdivided by a housing divider wall separating a secondary variable pressure and vacuum chamber combination from the primary chamber pair. A power piston is urged to move axially by the diaphragm(s) and actuates an output rod for operating the vehicle brakes through an engaged master cylinder.
It has long been known that the weight of a power booster can be reduced by using thin-wall or lightweight material for the housing walls. When this is done, some additional structural support is obviously needed to maintain the structural integrity of the housing. One manner of providing the additional structural support is to extend a shaft or shafts through the housing to carry the generated loads, freeing the housing shell from this function. When axial forces are generated in the power booster, the shaft(s) hold the relative positions of the front and rear housing walls.
One significant problem that arises when extending a shaft through the erstwhile hermetic chambers of a power booster, resides in a need to provide a secure, movable seal assembly where the shaft passes through the structure. This is complicated by the often desirable condition that the overall length of the power booster must be minimized. Accordingly, the sealing structure preferably avoids adding to booster length while concurrently providing an effective seal between relatively movable components. In the case of a tandem diaphragm vacuum power booster, the minimum theoretical length is equal to twice the space needed for the diaphragm and support wall travel distance, plus the thickness of the external housing walls, plus the divider wall thickness, plus the tolerances. In practice, approaching the minimum possible length has been difficult. Generally, the sealing mechanism undesirably adds to the booster length and may be difficult to assemble and expensive to produce. Accordingly, a new power booster sealing mechanism is needed.